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    <title>Document</title>
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    <script>
        var num = prompt("请输入年龄")
        if (num >= 30) {
            alert("带你去泡妞")
        } else if (num >= 20) {
            alert("带你去偷耳机")
        } else if (num >= 18) {
            alert("带你去网吧")
        } else {
            alert("滚，回去读书")
        }
    </script>
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